For background and contextual information, the above identified published patent applications and patents are referenced. Additionally, it is noted that some conventional systems for tracking and/or monitoring assets (herein generally referred to as “asset tracking systems”) utilize wireless tags that generally respond to any broadcast that is made. The wireless tags usually are passive, and the responses that the passive wireless tags make are often referred to as “chirps.”
More sophisticated conventional asset tracking systems utilize semi-passive wireless tags and/or active wireless tags. A semi-passive wireless tag includes an internal power source for transmitting, and an active wireless tag includes an internal power source for both receiving and transmitting. Semi-passive and active wireless tags generally have greater capabilities than passive wireless tags due to the internal power sources. Of course, power consumption is always a concern when a wireless tag includes an internal power source, since the internal power supply limits the useful life of the wireless tag, after which time maintenance is required (e.g., replacement of the internal power source).
In improved asset tracking systems, such as disclosed in U.S. Pat. No. 6,934,540 and other of the above-incorporated patent applications and patents, a wireless tag responds to a broadcast if the broadcast includes a common designation matching a common designation of the wireless tag. Such a common designation may comprise, for example, an “asset class” associated with the wireless tag. Ad hoc networks further may be created based on such classes, which ad hoc networks are referred to as “class based” networks.
Class based networks (and common designation networks in general) are beneficial because, in such networks, a communication device, such as a wireless tag, generally only transmits a response to a broadcast if the broadcast includes a class (or common designation) that matches a class (or common designation) of that communication device. Indeed, in a communication device employing a wakeup sequence of one or more of the patent references incorporated herein by reference, such communication device does not even process a broadcast once it is determined that the broadcast fails to include a matching class of the communication device. Consequently, the internal power supply of a semi-passive or active communication device is not drained by needless processing and/or responses to broadcasts.
In any asset tracking system, it often is important to know the physical location of an asset. This could include knowing where the asset is within a limited physical area, such as a warehouse; this also could include knowing where the asset is within several different warehouses in several different geographical locations, as well as where the asset is during transit between such locations.
In some conventional asset tracking systems in which wireless data communication devices are placed on the assets, a method for acquiring visibility of the assets includes broadcasting within an area at regular intervals in order to solicit responses from all of the wireless data communication devices within the area. The responses from the wireless data communication devices reveal the presence of the wireless data communication devices and, by assumption, the presence of the assets in the area. This method is not advantageous because the regular, repetitive broadcasts result in an unnecessary power drain of the responding wireless data communication devices when such devices comprise active or semi-passive radios. Moreover, interference also can occur if a large number of wireless data communication devices respond at the same time, thereby making it difficult to accurately identify all of the wireless data communication devices within the area that respond to the broadcast.
In an alternative conventional method, a timer is included with each wireless data communication device and the wireless data communication device is configured to transmit at periodic intervals as a function of the timer. The wireless data communication device thereby alerts the tracking system as to the whereabouts of the wireless data communication device and by assumption, the asset with which it is associated. By including timers with the wireless data communication devices, the wireless data communication devices may transmit at different times in order to avoid unnecessary interference. A wireless data communication device also can be set to sleep during intervals of no transmissions and to be awoken by the timer for making regularly scheduled transmissions. This increases the useful life of the wireless data communication devices because the wireless data communication devices do not consume power by actively listening for broadcasts while sleeping.
While this alternative method permits determinations as to the delivery and continued presence of an asset at a particular area, this alternative method does include drawbacks. For instance, by using timers, the wireless data communication devices are usually inaccessible by the asset tracking system during the sleep periods. Another drawback is that the wireless data communication devices automatically awake and transmit without regard to their location and without regard to whether the transmissions are actually warranted or even desired. In this respect, during transportation on a plane, for example, a wireless data communication device may awaken and transmit, thereby causing unwanted interference with the operation of the plane. Preprogrammed transmissions at regular intervals also may reveal the presence of the asset to unauthorized persons snooping for such radio transmissions.
Yet another alternative method for determining presence is disclosed and described in U.S. patent appl. publ. no. US 2007-0155327, incorporated herein by reference above. In accordance with an inventive aspect of the '327 application publication, a radio frequency (RF) communication device operates in at least two states.
In the first state, the RF communication device responds to a radio frequency transmission that includes data representative of an inquiry as to the presence of RF communication devices within an area. The “data representative of an inquiry as to the presence of radio frequency communication devices within an area” simply may be a predefined value in a particular format within the broadcast in accordance with a predefined protocol. A radio frequency transmission that includes such data is sometimes referred to therein as a “Present Broadcast.” The response to the Present Broadcast is made by the RF communication device by making a radio frequency transmission that includes an identification of the RF communication device. A radio frequency transmission that includes an identification of the RF communication device making the transmission, and that is made in response to a Present Broadcast, is sometimes referred to therein as a “Present Response.”
In the second state, the RF communication device does not respond to a Present Broadcast with a Present Response; specifically, no response to a Present Broadcast comprising a radio frequency transmission is made that includes an identification of the RF communication device, and preferably, no response to a Present Broadcast comprising a radio frequency transmission is made at all, whether including an identification of the RF communication device or otherwise.
The electronic components of the RF communication device are arranged and configured such that the RF communication device enters the second state from the first state upon responding to a Present Broadcast with a Present Response. The electronic components further are arranged and configured such that the RF communication device enters the first state from the second state upon receiving, through a sensor interface thereof, a sensor signal based on sensor-acquired data that is indicative of a predetermined condition. The sensor signal itself may include the sensor-acquired data or may be representative of the sensor-acquired data and may indicate, for example, a state of the sensor or movement of the RF communication device. In any event, such sensor signal is deemed to provide “sensor-acquired information” through the interface. The electronic components also further may be arranged and configured such that the RF communication device enters the first state from the second state upon receiving an instruction to do so, and the electronic components further may be arranged and configured such that the RF communication device enters the second state from the first state upon receiving an instruction to do so. The electronic components also further may be arranged and configured such that the RF communication device enters the first state after a predetermined period of time has passed or after a predetermined number of failed attempts to communicate by the RF communication device have occurred.
While these approaches represent solutions to determining presence, needs remain for still yet further improvements in methods for determining presence.
This, and other needs, are addressed by one or more aspects of the present invention.